Missile mounted circular slot antenna



Jan. 15, 1963 c. w. HORTON 3,074,063

MISSILE-MOUNTED CIRCULAR SLOT ANTENNA Filed March 5, 1954 4 SheetsSheet 1 FIG. 5.

CRYSTAL DETECTOR (EH-THREADED HOLE I N o D GIL :3 C O INVENTOR CLAUDE m HORTON Jan. 15, 1963 c. w. HORTON MISSILE MOUNTED CIRCULAR SLOT ANTENNA Filed March 5, 1954 4 Sheets-Sheet 2 INVENTO CLAUDE W. HORTON ISSILE) EORNEYS Jan. 15, 1963 Filed. March 5, 1954 C. W. HORTON MISSILE MOUNTED CIRCULAR SLOT ANTENNA 4 Sheets-Sheet 3 0 BIG. :0

2880 zlo 0 292 290 10 5 256 fi go THEOR EXPERTMENT 150 110 200 210 220 220 210 200 190 110 I60 1:10 140 PATTERN IN A PLANE CONTAINING THE AXIS OF THE CYLINDER (MISSILE). INVENTOR PROBES ARE ALL ON SAME SIDE OF THE SLOT.

6L AUDE W. HORTON ATTORNEYS Jan. 15, 1963 c. w. HORTON W N ATTORNEYS m w. W. Ea. wf

Unite States The present invention relates generally to antennas. More specifically it relates to an improved antenna for guided missile use.

The problem of designing an antenna suitable for use with a supersonic guided missile is a difficult one. The long, slender ogive required for missiles operating at supersonic speeds does not lend itself well to antenna mounting; any obstructions on the missile surface produce drag which cannot be tolerated. It is usually desirable, however, that the radiation pattern of the antenna be directed forwardly of the missile, at angles calculated to achieve optimum target sensitivity, with consequent maximum missile lethality.

One of the principal objects of the present invention, therefore, is to provide an antenna for a supersonic aerial missile, which will be mounted flush with the surface of said missile so as not to increase air drag thereon.

Another object of the invention resides in the provision of an antenna for supersonic aerial missiles, which will produce lobe patterns directed so that optimum target sensitivity, with consequent missile lethality, will be secured.

A further object of the invention is to provide a missile antenna which is characterized by extreme simplicity of design and which will occupy a minimum amount of space on the missile.

Other objects and many of the attendant advantages of this invention will be appreciated readily as the same becomes understood by reference to the following detailed description, when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a detail perspective view of a missile, with the improved antenna of the present invention installed thereon;

FIG. 2 is an enlarged detail section through the portion of the missile containing the improved antenna, and showing particularly the construction of said antenna and how it is arranged on the missile;

FIG. 3 is a diagrammatic representation of the improved antenna;

FIG. 4 is a detail bottom view of the antenna, showing the location of the energy transfer probes and the fastening screws with respect to the slots;

FIG. 5 is a block diagram showing the new antenna connected to a portion of a receiving system in a missile;

FIG. 6 is a detail perspective view broken away to show the location of the energy transfer probes at alternate sides of adjacent slots;

FIG. 7 is a view similar to FIG. 6, but showing an alternative arrangement of the probes, that is, on corresponding sides of the slots;

FIG. 8 is a graphic representation showing theoretical and experimental patterns produced by the antenna mounted in a plane containing the axis of the missile, with the energy transfer probes of alternate slots on sides opposite from the probes of adjacent slots;

FIG. 9 is a view similar to FIG. 8, but showing patterns (theoretical and experimental) produced with the probes on corresponding sides of the slots;

FIG. 10 is a graphic representation showing theoretical and experimental patterns in the plane of the antenna with the probes on corresponding sides of the slots;

FIG. 11 is a graph showing an experimental pattern atent shrines Patented Jan. 15, 1953 in the plane of the antenna with the probes on opposite sides of alternate slots from the probes of adjacent slots; and

FIG. 12 is a diagrammatic representation showing the geometry of a plane wave approaching the antenna from any direction.

Basically, the improved antenna which constitutes the present invention consists of a section of standard waveguide formed into a circle. In a tested embodiment the antenna thus formed was of 13 inches outside diameter, and had formed along the center line of its outer wall a plurality (41) of spaced oblong slots inch long, /8 inch wide and 0.928 inch apart. The slots were electrically excited by probes constituted by screws extending into the waveguide beside the slots, and midway of their lengths, a probe having been provided for each slot. Tests were made with the probes all on corresponding sides of the slots, and other tests were conducted wherein the probes were staggered with respect to the slots, that is, with alternate probes on opposite sides of the slots from probes of adjacent slots. Threaded holes were provided in the waveguide for receiving the probes, one such hole having been located on each side of each slot, removed inch from the center line. Since but one probe was needed for each slot, holes not used for probes received fastening screws, the ends of which terminated flush with the inner surface of the waveguide so as not to obstruct the flow of energy in the antenna.

For the purpose of making pattern measurements, the confronting ends of the waveguide section constituting the antenna were bent outwardly and conventional waveguide connectors were attached thereto. A well-matched resistive termination was connected to one of the outwardly bent portions and a receiver was connected to the other of said bent portions. The antenna was mounted about the outer surface of a steel pipe simulating a missile, and the ,missile was placed in a horizontal position, with said antenna oriented so that the connections were at the bottom. Measurements in the plane containing the axis of the missile were obtained by rotating the pipe about a vertical axis through its center. Measurements in the vertical plane containing the antenna were made by rotating said antenna by hand about the circumference of the pipe. As will be obvious, when applied to a guided missile, the antenna would be terminated within the missile; that is, there would be no outwardly bent portions.

A number of the circular antennas may be used on a single missile to form an antenna system, with the antennas defining the system arranged in such a manner that the major lobes, for signal emission or response, will be sharpened and steered forwardly (or backwardly) of the missile, as desired. Such a system will have a maximum sensitivity for targets in a belt nearly at right angles to the axis of the missile and zero sensitivity for targets substantially parallel to the missile axis. In a plane at right angles to the axis of the missile the pattern has as many lobes as there are slots in the antenna, and the nulls between the lobes are sufi'iciently well defined to enable the antenna to be used as a part of a rate-ofroll measuring system. In this patent application, however, but one antenna has been shown, for purposes of simplicity.

Referring now more particularly to the drawings, an aerial missile is designated generally by the numeral 10, said missile having an ogive 11.

Surrounding the missile 10 at the inner extremity of the ogive 11 is the antenna 12 which constitutes the present invention.

The antenna 12, as best seen in FIG. 6, includes a body comprised of a section of conven-,

.tional waveguide, of rectangular cross-section, formed into substantially circular shape with closed abutting ends. As best seen in FIG. 2, the meeting end portions of, the missile it; and ogive llmay be turned inwardly to define flanges 13 forming the base of a recess 14 to receive the antenna with the outer surface of said antenna flush with the outer surface of the missile. The flanges 13 receive securing screws 15 which extend into the antenna for retaining it in the recess, certain of said screws, however, being relatively long and constituting energy transfer probes 16. The screws 15, with the antenna 12, also function to connect the outer skin of the missile 10 to that of the ogive. It should be understood, however, that the illustration provided by the drawings is to a great extent diagrammatic and 'that in actual practice means other than the antenna could be employed to retain the missile and ogive in proper operative relation.

Formed in the outer surface of the antenna is a plurality of slots 17, arranged in an annular series. The slots 17 are, as best seen in FIG. 4, of oblong contour and so arranged that the probes 16 are positioned to terminate with their free ends in spaced relation to the inner surfiace of the antenna and medially of the lengths of said slots and on alternate sides thereof (FIG. 7). As best seen in FIGS. 6 and 7, the ends of the screws which are not used for probes have their inner ends terminating flush with the inner surface of the bottom wall of the antenna so as to produce no interference to energy flowing in said antenna. If desired, the slots 17 may be filled with plastic material to eliminate the possibility of their producing shock waves.

The slots 17 are each of a length corresponding to one-half wavelength in air at the transmitting or receivingfrequency, for example, 3.2 centimeters, and each slot has a lobe pattern with, theoretically, nulls between each said pattern. In FIG. 2 at X is shown diagrammatically radio transmitting or receiving equipment mounted in the missile. The apparatus X is shown connected to one of the probes 16, the connection being made adjacent one of the closed ends. As shown in FIG. 5, the receiving equipment is connected to the antenna through a crystal diode 18 at one of the closed ends, and a resistive load 18a terminates the other closed end. The output of said receiving equipment is proportional to the rate of change of the angular bearing of the source of waves to the axis of the antenna. In the arrangement of FIG. 3, the antenna is terminated at each end by a diode; a diode 19 provides a resistive termination and a diode 20 functions as a detector;

In discussing the theory of operation of the improved antenna, reference is made to FEB. 12. The X-Z plane is chosen so that the direction of travel of the plane wave lies in it. For convenience the location ofthe slots is chosen so that one of them, say slot #0, falls on the X-axis. The difference in phase, Ap, between the wave received by the slot and any other slot, say slot #k, at an angle, x11, from the X-axis, is seen to be:

a=outer radius of the wave guide (antenna) A =wave length in air Q=angle between the axis of the missile and the direction from which the wave approaches (direction of the Wave).

The signal which arrives at the crystal detector 18 mounted at one end of the antenna will be the vector sum of the contributions of the individual slots, expressed as:

+N Z) :1: F iwti(21ra/Mir)(1-cos tPn) sin a n= N Where the summation is taken over all of the slots and I represents the responses of the individual slots to the plane wave being received.

The results of theoretical and experimental work, embracing 23 energy transfer probes (and associated slots) of a circular antenna made pursuant to the present invention, are illustrated graphically in FIGS. 8 through ll of the drawings.

In F113. 8 is shown the pattern of the antenna measured in a plane containing the axis of the missile about which said antena extends, and with the probes mounted on opposite sides of alternate slots. This view also shows the theoretical pattern for the same conditions, which is seen to be an envelope of the experimental pattern in the forward half-circle. The response in the back halfcircle was found to be less, due to the obstruction caused by the rotatable mount on which the test missile was positioned. The numerous interference fringes in the experimental pattern were probably caused by the diffracted wave that travelled around the end of the missile to slots at the rear.

FIG. 9 illustrates the pattern measured in a plane containing the axis of the missile with all of the probes located on the same sides of the slots, and also shows the theoretical pattern under the same conditions. It will be seen that although the general agreement was good, the deep nulls predicted by the theory were not found on the experimental pattern. Moreover, the interference fringes were more numerous in this pattern than in the one of FIG. 8. It should'be noted that the axis of the' missile was oriented 90 degrees to that shown in FIG. 8.

FIG. 10 shows experimental and theoretical patterns developed by the antenna positioned in a plane normal to the axis of the missile, and with the probes on corresponding sides of the slots. Both patterns agree in having a regular alternation of lobes and nulls, the separation of successive lobes being equal to the separation of the slots.

FIG. 11 illustrates the pattern developed along the equatorial plane of the antenna (the plane at right angles to the missile axis) with the exciting probes mounted on alternate sides of the slots. This pattern differs substantially from that obtained when the probes are mounted on corresponding sides of said slots. In the pattern shown in FIG. 11, the lobes are separated 16 and the nulls are only down 3.5 db. This contrasts strongly with the pattern shown in FIG. 10, in which lobes are separated only 8, while the nulls are down 12 db.

It should be understood, with respect to FIGS. 8 through 11, that the theoretical treatment is approximate in that the eitect of the missile body (metallic cylinder) on the wave field is neglected and that the response of those slots not in a line-of-sight is also not considered. Moreover, the experimental patterns in the plane containing the axis of the missile (FIGS. 8 and 9) may be somewhat modified from the expected theoretical form by the outside connections, because these connections are in lineof-sight to the excitation source. The experimental patterns would be different if the antenna had been mounted with its outer wall flush with the surface of the cylinder, and if the ends had been terminated within said cylinder.

What is claimed is:

1. In a missile, a circular antenna surrounding the missile and having a hollow body of rectangular cross-section, said body having a peripheral wall positioned flush with the outer wall of the missile and having an annular series of spaced slots each having a length equal to onehalf a given wavelength in air, and radiation pattern determining means in the antenna, said means cooperating with said slots for transferring electrical energy in predetermined patterns about the antenna.

2. The antenna recited in claim 1, including additionally resistive means electrically terminating the antenna at a given point on its circumference, and feed means connected to a second point on the antenna, said second point being in close spaced relation to but electrically isolated from said first point.

3. An antenna for a missile comprising a wave guide portion of rectangular cross-section and closed at each end and of circular shape, said antenna having said closed ends in abutting relation, spaced slots formed in the peripheral wall of the wave guide portion and being arranged in an annular series, each said slot being of a length equal to one-half a given wavelength in air, and energy transfer means mounted on the inner Wall of the wave guide portion and extending toward said peripheral wall and terminating in spaced relation to said slots at corresponding sides thereof and medially of their lengths, said means and slots cooperating for transferring electrical energy in predetermined patterns about the antenna.

4. An antenna as recited in claim 3, including additionally means for electrically terminating the antenna at a point on its circumference, and feed means connected to a second point in close spaced relation to but electrically isolated from said first point.

5. In combination with a missile having an ogive, said missile and ogive having outer walls shaped to define an annular recess, an antenna in the recess, said antenna being hollow and of circular contour and rectangular cross-section, said antenna having a peripheral wall lying flush with the outer Walls of the missile and ogive, slots in the peripheral wall of the antenna and arranged in an annular spaced series, means connected to a given point on the circumference of the antenna for transferring energy to or from said antenna, and means for terminating the antenna at a second point on the circumference of the antenna spaced and electrically isolated from the first point.

6. The combination recited in claim 5, wherein said terminating means is constituted by a crystal diode and said energy transferring means is constituted by radio transmitting or receiving equipment.

7. In combination with a missile having an outer wall, an antenna extending about the circumference of the missile and comprising a hollow body having an outer surface disposed to lie rfiush with the outer surface of said outer wall, said antenna having a slot, and a probe mounted in the antenna to cooperate with said slot for transferring electrical energy in predetermined patterns about the antenna.

References Cited in the file of this patent UNITED STATES PATENTS 2,527,100 Kihn Sept. 9, 1947 2,523,455 Stewart Sept. 26, 1950 2,596,480 Guptill May 13, 1952 2,637,814 Johnson May 5, 1953 2,648,839 Ford Aug. 11, 1953 2,679,590 Riblet May 25, 1954 2,764,756 Zaleski Sept. 25, 1956 2,781,500 Armstrong Feb. 12, 1957 2,781,512 Robinson Feb. 12, 1957 OTHER REFERENCES Slot Aerials, Wireless World, February 1948, pages 57, 58. 

3. AN ANTENNA FOR A MISSILE COMPRISING A WAVE GUIDE PORTION OF RECTANGULAR CROSS-SECTION AND CLOSED AT EACH END AND OF CIRCULAR SHAPE, SAID ANTENNA HAVING SAID CLOSED ENDS IN ABUTTING RELATION, SPACED SLOTS FORMED IN THE PERIPHERAL WALL OF THE WAVE GUIDE PORTION AND BEING ARRANGED IN AN ANNULAR SERIES, EACH SAID SLOT BEING OF A LENGTH EQUAL TO ONE-HALF A GIVEN WAVELENGTH IN AIR, AND ENERGY TRANSFER MEANS MOUNTED ON THE INNER WALL OF THE WAVE GUIDE PORTION AND EXTENDING TOWARD SAID PERIPHERAL WALL AND TERMINATING IN SPACED RELATION TO SAID SLOTS AT CORRESPONDING SIDES THEREOF AND MEDIALLY OF THEIR LENGTHS, SAID MEANS AND SLOTS COOPERATING FOR TRANSFERRING ELECTRICAL ENERGY IN PREDETERMINED PATTERNS ABOUT THE ANTENNA. 